flood modeling and flood forecasting using...

|| Volume 5 || Issue 6 || June 2020 || ISSN (Online) 2456-0774

INTERNATIONAL JOURNAL OF ADVANCE SCIENTIFIC RESEARCH

AND ENGINEERING TRENDS

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FLOOD MODELING AND FLOOD FORECASTING USING

HEC-RAS

Avanti Waghchaure1, Aarti Patil2, Pragati Bachhav3, Rajashri Bodhai4

Student, Civil Engineering Department, Sinhgad Academy of Engineering, Kondhwa, Pune1,2,3,4

Prof. G.S Patil5

Professor, Civil Engineering Department, Sinhgad Academy of Engineering, Kondhwa, Pune5

[email protected], [email protected], [email protected], [email protected],

[email protected]

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Abstract: - The flood and drought condition in our country has been more frequent in past few years due to changing

climatic conditions of the environment. Prediction of stage of river during the flood requires mathematical modeling of the

river. This helps to take decision related to the flood protection and disaster management work in that area. In

Maharashtra, Pune city faces problems of floods and damages during monsoon. Many bridges over rivers get submerged,

resulting failure of communication facility, inundation of the city and surrounding area during this period. The flood

prediction of Mutha River using HEC-RAS has discussed in this paper. This will be helpful for preparation of flood

mitigation plan for Pune city as a curative measure for the control of flood in the Mutha River. This model also provides the

depth of water, velocity as well as water surface elevation with respect to time. The study represents the importance of 2D

modeling of flood problems which helps to develop management strategies to tackle the probable future events by employing

flood risk reduction measures.

Keywords: - Mutha river, Flood modelling, Flood forecasting, HEC-RAS.

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I. INTRODUCTION

1.1 General

Water is an essential ingredient of life. Since the beginning of

the existence of mankind, drought and floods have affected

human activities throughout the world. River line floods are the

floods caused by the water overflowing from the river banks

into the flood plains. Flood is the most prominent natural

hazard in India and its frequency is higher than any other

natural calamities. They have catastrophic impact on lives as

well as property. The water carrying capacity of the river has

obviously reduced over the years. There are many reasons and

factors responsible for it. Due to encroachment, silting and

scouring, depth and width are reducing day by day. As the

overall carrying capacity has decreased, it causes floods.

During monsoon, when the reservoirs get filled to its maximum

limit, the water is discharged from the dam. When the water is

released from the dam, the river cannot contain the water inside

it and thus the water comes out causing floods. So to calculate

the total water carrying capacity, firstly we need to know the

nature and depth of river basin. This paper involves the study of

the river’s cross-section and finds the carrying capacity and

other important parameters and also generates warning for the

areas under risk that require immediate attention. By reducing

carrying capacity on adjoining areas and modifying the channel

it will be helpful for preparation of flood mitigation plan for

Pune city as a curative measure for the control of flood in the

Mula-Mutha River. Thus, modification of river channel should

do to increase the carrying capacity of the rivers in Pune and

thus reducing the effect of flood in Pune city and surrounding

region. In view of that, various flood protective works should

carried out by strengthening and raising the height of existing

of embankment or retaining wall by 2 to 3 meters so as to

protect the city against the heavy flood in future.

1.2 Aim of the study

To analyze the flood carrying capacity of the segment of

Mutha river between Mhatre Bridge and Joshi Bridge which are

1.6 km apart by evaluating its capacity in response to discharge

and slopes by using the HEC-RAS software.

1.3 Objective of the study

To compute the different cross-section using past

flood data, discharges and HEC-RAS.

To determine adequacy of existing section to a carry

flood of various magnitude.

mailto:[email protected],%[email protected]

mailto:[email protected]

mailto:[email protected]




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To recommend measures to assure safe flood

conveyance for the study reach by increasing height of

retaining wall, proposing new bunds or retaining wall.

To identify critical section for the spread of water in

the study area.

1.4 Study Area

Pune district lies in Bhima basin. Mula, Mutha, Pawana, Ram

and Dev river are the five rivers that flow through Pune city.

Mula and Mutha river meet at the College of Engineering,

Pune. The origin of Mutha is in the lower hill ranges of eastern

flanks of N-S trending Sahyadri ranges, which flows towards

eastwards and then SE-wards up to Khadakwasla and then it

turns in NE direction to flow in nearby plain area until it meets

Mula river at Sangam in Pune city. It is found that flood

problem in Pune city is generally caused due to flood water

releases from various dams located on upstream side of Pune

city on Mutha River. Our study area consists of the part

between Mhatre Bridge to Joshi Bridge. This part consists of

total 66 river stations which we have studied. Depending on the

hydraulic properties of flood water which have generated by

software, required changes in design of river basin are

mandatory if any.

1.5 Limitations of Study

Data availability is a major problem for this project.

Data has to be collected from the respective

government department which is a cumbersome

process.

Handling the software and using it for the project is

also quite difficult and time consuming. Handling the

software can be very challenging at times.

Difficulty in understanding information. The data we

get from government bodies is raw and not very

understandable. Therefore much time is required to

understand the data and sort it according to our

requirements.

Learning software is time consuming. It is a very

different platform and requires a thorough

understanding for being able to use it and derive

required outputs.

1.6 Research Methodology

Pune faces the flooding problem each year. So flood forecasting

is important. There are many types of software which can use

for flood modeling and flood forecasting. Some of the

softwares are,

HEC-RAS (Hydrologic engineering centre river

analysis system)

HEC-HMS(Hydrologic engineering centre hydrologic

modeling system)

ARC-GIS (aeronautical reconnaissance coverage

geographic information system).

Due to ease in getting required data and handling of software,

we choose HEC-RAS. It is freely available software developed

by US Army Corps of Engineers and it can perform one- and

two-dimensional hydraulic calculations for a full network of

natural and constructed channels.

1.6.1 HEC-RAS

The hydraulic model used for our study is based on Hydraulic

Engineering Center’s River Analysis System (HEC-RAS),

version 5.0.1. It is freely available developed by US Army

Corps of Engineers and can perform one- and two dimensional

hydraulic calculations for a full network of natural and

constructed channels. The HEC-RAS model is one of the most

commonly utilized floods modeling software in hydrodynamic

simulation. This model has designed to perform 1D steady flow

as well as 2D unsteady flow simulations for a river flow

analysis, and sediment transport and water temperature/quality

modeling. The model uses geometric data representation as

well as geometric and hydraulic computation routines for a

network of natural and constructed channels of river.

The software that we used i.e. HEC-RAS has ability to make

the calculations of water surface profiles for steady and

gradually varied flow as well as for subcritical, super critical,

and mixed flow regime. HEC-RAS is also capable to do

modeling for sediment transport, which is notoriously difficult.

In HEC-RAS, there are various boundary conditions available

for steady flow and sediments analysis computations.

At each cross-section, HEC-RAS needed various input

parameters to describe shape, elevation, and relative location

along the river stream:

River station (cross-section) number

Reduced levels for each terrain point

Left and right bank station locations

Reach lengths between the left floodway, stream

Centre line, and right floodway of adjacent cross-

sections

Manning’s roughness coefficients

Channel contraction and expansion coefficients

Maximum discharge of the stream

Geometric properties of any hydraulic structure like

bridges, culverts, and weirs etc.

II. LITERATURE SURVEY

Literature survey is the most important part in any kind of

research. Before starting any paper, we need to study different

previous year research papers of our domain. It helps us to

predict and minimize the drawbacks in our study. In this section

we will thoroughly review previous year’s research papers.

In the paper of flood inundation simulation of

Mahanadi River, Odisha during September 2008 by using

HEC-RAS 2d model the sensitivity analysis carried out for

different manning’s coefficient ‘n’. Flood hazard maps




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prepared based on the flood depth of the Mahanadi River.

HEC-RAS 2D is a hydraulic model used to simulate water

flowing through rivers and open channels. It observed that the

model performed well for channel roughness coefficient of

0.020.

In the paper of prediction of flood for lower tapi river

using HEC-RAS, analysation of stability of segment of Lower

River performed. This helped for preparation of Flood

Mitigation Plan for Surat city. As the Surat city needed curative

measure for the control of flood in the river Tapi. In this paper,

uniform flow computed for past five year’s peak flood

discharge data. It concluded that, as the slope of river increases,

velocity of water also increases and hence the discharge

carrying capacity of river also increases.

In the paper, flood modeling by using HEC-RAS, the

main goal was to provide flood control system .They used

outputs to determine extent of overtopping of bridges. Flood

modeling system here presented copes with a basic need of

standardization of the databases system. The use of HEC-RAS

provided capability to simulate flood depth in different part of

the floodplain.

In the paper, floodplain mapping and management of

urban catchment using HEC-RAS: a case study of Hyderabad

city, a methodology for developing a flood model in urban

environment carried out. The hydraulic modeling with GIS

integration made the modeling process easy and produced more

easily understandable results. The flood inundation maps were

further processed in Arc-GIS to develop flood risk map and

papered on Google Earth imagery.

In the paper of river flood modeling using GIS, HEC-

Geo-RAS and HEC-RAS for Purna river, Navsari district,

Gujarat, India, the first part of the study followed by the Arc-

GIS and HEC-Geo RAS software in which pre-processing

completed which contain to develop D.E.M (digital elevation

model), Geo referencing, Shape file, Mosaic, Extract by mask

of Navsari district and Purna river. Then from the HEC-Geo

RAS geometry stream centerline, bank line, flow path and its

centerline and cross-section cut lines is defined.

III. METHODOLOGY

This chapter explains how to perform hydraulic analysis study

with the HEC-RAS software. It describes the methodologies

used in performing the one-dimensional flow calculations

within HEC-RAS. Steps for performing steady flow analysis of

Mutha river basin have explained below.

The terms used in software have explained in user manual of

the HEC-RAS software. User manual gives the clear idea about

what parameter is to enter in which block.

Figure 1: Flowchart of methodology

Step 1: To start a new HEC-RAS paper.

In the main window, open HEC-RAS click on the File, then

click on New Paper. In the window of New Paper, type in Title

and File name then click OK.

Figure 2: Project title window

Step 2: To set up river reach.

For a subcritical flow, which is very common in natural and

man-made channels, step computations will begin at the

downstream end of the reach, and progress upstream between

adjacent cross-sections. For supercritical flow, the

computations will begin at the upstream end of the reach and

proceed downstream.

In main window, click on Edit, then Geometric Data.

Figure 3: Main window




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Step3: Plan cross-sections

Figure out where to position the cross-sections, and then scratch

on the paper on the screen.

Figure 4: Geometric data view

Step 4: Enter cross-section data

Click on the cross-section. Click the Options. Choose “Add a

new cross-section.”

Figure 5: Cross-Section Data view

Step 5: Enter steady flow data

In main menu, click on Edit, then choose Steady Flow Data.

Enter the number of profiles. Ex. for 50-year flow enters 1.

Reach boundary conditions are the two most common options

used are normal depth and known water surface. For normal

depth condition, click Normal Depth, enter stream slope.

Figure 6: Steady flow data

Figure 7: Steady flow boundary conditions

Step 6: Steady Flow Analysis

On main window, click on Run option, after that click on

Steady Flow Analysis. After that in flow regime, select mixed

and the click on Compute.

Figure 8: Steady Flow Analysis




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Figure 9: HEC-RAS finished computations

Step 7: View Output

Click on View option on main window. There will be various

options as follows:

Cross Sections

General Profile Plot

XYZ Perspective Plot

Hydraulic Property Table

Detailed Output Table

Profile Summary Table

Summary Error, Warning, Notes

IV. RESULT

Results of the study consist of various profile plots, output

tables of hydraulic properties, XYZ perspective view which we

can rotate to any desired angle. From this result, we can design

the river basin as per requirements.

Figure 8: Cross section

The software can generate profile plots also called long sections

or longitudinal profiles of the HEC‑RAS steady flow and

unsteady flow computational results, displaying the water

surface elevation, energy grade line elevation, critical depth

elevation, channel invert, bank stations, structures and more.

Figure 9: Profile Plot

Figure 10: General Profile Plot- Velocities

Figure 11: General Profile Plot- Area




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Figure 12: General Profile Plot- Top width

Figure 13: General Profile Plot- Weighted n

Figure 14: General Profile Plot- Froude number

The user can define the starting and ending location for extent

of the plot. In order to get different perspectives of the river

reach, the plot can rotate left or right, and up or down.

Figure 15: XYZ Perspective plot

Figure 16: Cross section output

Distribution of flow in three subdivisions of the cross-section is

as follows:

Left overbank

Main channel

Right overbank




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Figure 17: Flow Distribution Output

Figure 18: Standard Table 1

Figure 19: Standard Table 2

Figure 20: Profile Output Table

Figure 21: Errors, Warning and Notes for Plan

V. CONCLUSION

This paper presents a methodology for modeling and

forecasting of flood caused due to many reasons like heavy

rainfall, poor river basin, and lack of space for rainwater flow

in riverbed due to urbanization. The use of HEC-RAS software

made the forecasting & modeling process easy and also

produced more easily understandable results. The cross-

sections of river bed were cross sections prepared in HEC-RAS.

The areas susceptible to flood have recognized by analyzing

XYZ perspective view and warning table simultaneously which

are developed by software itself. It is clearly seen that the cross-

section end points should extend vertically for the computed

water surface. Otherwise it will cause overflow of flood water

through river basin. Thus, our study area needs immediate

attention during flooding situations & should assign high

priority. The result table of hydraulic properties and all profile

plots can also be used in future planning of developmental

works. Present situation of river basin is not that capable to

carry huge flood. So it is very important to increase size of river




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basin horizontally as well as vertically. Following are warnings

developed by HEC-RAS:

Location:

River: downstream

Reach: upstream

RS: 20 Profile: PF 1

Warning: End points of the cross-section end points should

extend vertically for the computed water surface.

Warning: There is a need for additional cross sections because

the velocity head has changed by more than 0.5 ft (0.15 m).

REFERENCES

[1] US Army Corps of Engineers. HEC-RAS user manual

[2] Flood Inundation Simulation Of Mahanadi River, Odisha

During September 2008 By Using HEC-RAS 2D Model

(2019) by Tushar Surwase, G. Srinivasarao, P. Manjusree,

Asiya Begum, P. V. Nagamani And G. Jaisankar

[3] Prediction Of Flood For Lower Tapi River Using HEC-

RAS (2015) by Darshan Mehta, Dr.S.M,Yadhav,

Mrs.Sahita Waikhom

[4] Flood Modeling By Using HEC-RAS. (2017) by Azhar

Husain

[5] Floodplain Mapping And Management Of Urban

Catchment Using HEC-RAS: A Case Study Of Hyderabad

City by Vinay Ashok Rangari

[6] River Flood Modeling Using GIS, HEC-Georas And

HECRAS For Purna River, Navsari District, Gujarat, India

(2017) by Azazkhan I .Pathan, Prof. B.M Vadher, Dr .P.G

Agnihotri

[7] https://pmc.gov.in/en/pune-river-development.

[8] http://www.punefloodcontrol.com/flood%20control%20off

icers.html

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